The present invention relates to industrial sewing machines of the overlock stitch type, designed mainly for effecting an overedge stitch to cover the edge of a fabric. The edge thus being prevented from unraveling. Also, two or more thicknesses of fabric can be sewn together so that the overlock stitch sewing also embodies a joining of these thicknesses of fabric on their edges.
Sewing machines of the overlock stitch type are currently used for making undergarments, night lingerie (linen articles), polo jumpers, and more generally, articles made of jersey, of knitted material, or equally of all material presenting a certain elasticity.
Overlock stitch sewing machines generally comprise at least one needle reciprocating through the front end of a rearward open throat slot in parallel with a chain finger. Two loopers driven in combination with the needle, cooperate to form the overlock stitch sewing.
The overlock stitch sewing can be formed in the absence of the fabric underneath the needle, creating what is called a thread chain. Without particular precautions, this thread chain appears thus at the commencement and at the end of the overlock stitch sewing being sewn in the edge of the fabric.
In order to lessen, at least partly, the inconvenience of using this machine with the resulting increase of time and of the price of fabrication, it has been proposed to insert an initial thread chain into the overlock stitch sewing itself, so as to block or backtack. By so backtacking the end of the stitch, the tendency to open is substantially lessened.
In order to realize automatically this inserting of the thread chain, an overlock stitch sewing machine was equipped with a Union Special Corporation Machine -39600 means arranged in front of the needle and able to retain the free end of this thread chain until it could be sewn into a fabric means.
It has appeared, nevertheless, that this equipment is not always satisfactory. In fact, the presence of a cutting device with blades in front of the needle, in alignment with the chain finger, does not permit the immediate positioning of the fabric in front of the needle, when the cutting blade is in its low position. The overlock stitch sewing is thus started on the edge of the thread chain itself, even before the material arrives under the needle. Such a premature function of the overlock stitch creates the appearance of a loop or an accumulation of ugly looking stitches at the edge of the sewn fabric.
In order to prevent such a defect, the machine is stopped with the cutter blade in a raised position. It is then possible to introduce the pieces of material, after lifting the presser foot, just up to the needle. The overlock stitch sewing is then carried out immediately across the edge of the material and the thread chain is then progressively sewn in.
This solution, which is applied at the present in a majority of machines presents the drawback of being very expensive. It also necessitates the use of a special driving motor comprising a stopping device associated with the motor shaft, so that the motor always stops in the same position. Such a motor is expensive and greatly increases the price of the overlock stitch sewing machine.
It is therefore an object of this invention to provide an apparatus which permits a satisfactory insertion of thread chain without the need of such a driving motor.
Another object of this invention is to provide a throat plate housing means which allows the thread chain to be positioned whereby further formation thereof is prevented.
Still another object of this invention is the provision of a depression or groove in the edge of the throat plate adjacent the throat slot for positioning and retaining a thread chain to avoid accidental cutting thereof by the knives.